The proposed studies are a continuation of an interrelated series of experiments in rats designed to increase our understanding of how disturbance of the mother-infant relationship affects the developing young and may predispose to behavior disorder and stress-induced disease in later life. This animal model system facilitates the discovery of new hypotheses regarding the biological processes which are responsible for the increased risk of illness, both medical and psychiatric, known to be associated with humans recently deprived of close social relationships, important goals and familiar environments. The disciplines involved are those of experimental psychology, biology and psychophysiology in particular, as adapted to immature experimental animals. The methods include selected electrophysiological, pharmacological, and microsurgical techniques as well as behavioral observation and recording. The aims are to understand the specific processes or mechanisms by which the experience become translated into altered physiological and behavior development. The proposed studies focus upon four aspects of the problem: 1) The nature of social attachment system of the young rat, separation distress (ultrasonic vocalization in particular), and the process of its alleviation by reunion with social companions. 2) The slower developing effects of separation, which depend upon withdrawal of behavioral, nutritional, thermoregulatory, olfactory and tactile regulatory processes hidden within the exchanges of the mother-infant relationship. Alterations in autonomic cardiovascular regulation, behavioral reactivity levels, sleep wake state organization and suckling will be analyzed. 3) The impact of these processes on the incidence of prolonged sleep apneas, bradycardias and unexpected death which we have recently found to occur after baro- and chemo-receptor denervation in young rats, a model of the 'sudden infant death syndrome'. 4) How these processes become translated into developmental outcome: altered maternal behavior and susceptibility to experimental hypertension in particular.